public static void main(String[] args) throws Exception {

System.out.println(new ValidPalindrome().isPalindrome("989 "));

}

public boolean isPalindrome(String s) {

if (s == null || s.isEmpty()) return true;

s = s.toLowerCase();

for (int i = 0, j = s.length() - 1; i < j; ) {

char f = s.charAt(i);

char l = s.charAt(j);

if (!(f >= 'a' && f <= 'z') && !(f >= '0' && f <= '9')) {

i++;

continue;

}

if (!(l >= 'a' && l <= 'z') && !(l >= '0' && l <= '9')) {

j--;

continue;

}

if (f != l) return false;

i++;

j--;

}

return true;

}